Cigarette smoking, coffee and alcohol use were investigated prospectively in 37 high-dose benzodiazepine (BZD) regular users (HDRU), 87 low-dose BZD regular users (LDRU), 50 low-dose BZD occasional users (LDOU) and in 37 non-BZD users (control subjects). The frequency of smokers was significantly greater in the HDRU than in the other three groups studied. Also, the HDRU consumed a significantly greater number of cigarettes and dose of caffeine per day than the other subjects investigated. Also, alcohol dependence was significantly more frequent in the HDRU. Regression analysis showed a significant positive correlation between the BZD dose and both the cigarettes and the caffeine consumed per day. The findings suggest that BZD should be prescribed with caution in individuals who are heavy smokers or are consuming large amounts of coffee and alcohol.